ASoC: rsnd: add CTU (Channel Transfer Unit) prototype support

This patch adds CTU (Channel Transfer Unit) support for rsnd driver.
But, it does nothing to data at this point, but is required for MIX
support.

CTU design is a little different from other IPs (CTU0 is including
CTU00 - CTU03, and CTU1 is including CTU10 - CTU13, these have different
register mapping) We need to care about it on this driver.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>